Hitherto, transfer presses have been designed to have a plurality of working stations in a press main body so that workpieces are successively transferred from one station to the next station by means of a transfer feeder acting between these stations, whereby the workpieces are worked into a final form. In general, the arrangement is such that the first stage, constituted by a drawing press, is followed by second and subsequent stages which are constituted by presses for conducting various additional works, such as trimming, piercing, and so forth.
Transfer presses are also known in which a crown, a slide, and a bed are assembled together to form a press unit having a modular structure, and a plurality of such press units are suitably combined in accordance with the required specifications of the press work (refer to, for example, Japanese Patent Laid-open No. 2-247031). This approach facilitates modification or change of specifications to cope with the diversification of needs, thus offering widened use, as well as a reduction in the cost and an increase in the efficiency of transportation, of transfer presses. A transfer press of the type described is constructed such that successive stages of the press process employ separate crowns, as well as separate beds, and each crown is supported by uprights, wherein one upright is disposed at each side of the connecting surfaces of each of the adjacent crowns and beds. Alternatively, the arrangement is such that, as shown in FIG. 10, a single common upright 53 is disposed on the connecting surfaces of the adjacent crowns 55, 55 and beds 51, 51.
In order to fasten the crowns 55, the upright 53, and the beds 51, a pair of tie rods 56 are inserted into a pair of tie-rod bores extending through these members, and nuts 57 are screwed to and tightened on the upper and lower ends of the tie rods 56, thereby fastening these members. Although not shown, mounting pieces (locating means) are provided on the surfaces of the crowns 55 and the beds 51 at which they are connected to the upright 53, in order to eliminate any positional deviation. In order to minimize the feed stroke for the workpieces, the transfer press of the type described employs an idle station 58 disposed at a position which is at the midpoint of the distance A between the dies of the adjacent stages, i.e., behind each upright 53 which appears at the front side. The idle station has the function of temporarily storing workpieces which are to be fed to the subsequent stage of the process.
In this type of transfer press, a pair of tie rods 56 are received in each upright 53 which is commonly possessed by two adjacent stages of the process, so that the upright inevitably has a large width in the direction of the press line. This inconveniently increases not only the weight but also the feed stroke of the workpiece 60. Consequently, the following problems are encountered:
(1) In order to preserve the feed stroke at a level not greater than a predetermined value, it is necessary to provide each idle station 58 with an idle nest (attachment) 59 for holding the workpieces 60, so that the overall length of the press line is increased. The crowns 55 and the beds 51 of adjacent stages are fastened together by means of a pair of tie rods 56. Consequently, the total weight of the upright 53 and the tie rods 56 is increased and, in addition, the production cost is raised due to the necessity of drilling a pair of elongated bores for receiving the tie rods 56. PA1 (2) Provision of the idle nest 59 between adjacent stages of the process requires a space of a certain length large enough to store the workpieces 60, resulting in a further increase in the feed stroke. Consequently, the above-mentioned distance A between the dies of the adjacent stages and, accordingly, the overall length of the press line are increased. PA1 (3) Preparatory work for changing the idle nests 59 is necessary in accordance with a change in the type of products to be obtained. This, however, requires a troublesome work and poses problems with regard to safety, due to the fact that the idle nests 59 are disposed behind the front uprights 53. PA1 (4) Use of a large number of idle nests 59 enhances the risk of automatic stopping of the press due to, for example, deviation of the position of a workpiece. PA1 (5) In general, the second and subsequent stages perform trimming and piercing, so that reusable sheet materials or intended small articles are generated. It is, however, not easy to take such sheet materials or small articles out of the idle station, because the upright has a large width.
An art as shown in FIG. 9 has been proposed in order to reduce the length of the press line (refer to, for example, Japanese Patent Laid-Open No. 5-177399). In this art, a plurality of beds 51, 52 in the form of segments are arranged end-to-end and a plurality of uprights 53 are provided so as to protrude from these beds 51, 52. These uprights 53 carry segments of support beams 54, which in turn carry crowns 55 of the respective stages arranged in the form of girders spanning these beams 54. The beds 51, 52, the uprights 53, the support beams 54, and the crowns 55 are fastened together by means of tie rods (not shown) which penetrate all or some of these members.
This type of transfer press, however, suffers from a problem in that, since the frames constituted by the support beams 54 in support of the crowns 55 and the bed 52 of the second section are large and heavy, a troublesome work is required to disassemble the whole press into sections of sizes and weights which fall within the limits posed in transportation.